Bio-fabrication of ZnO films using plants, enzymes, and microorganisms has been recognized as an environmentally friendly procedure as an alternative to physical and chemical methods. In this research, the optical and structural properties of ZnO thin film have been investigated using UV-Vis spectrophotometer, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The ZnO films was prepared by spin-coating the mixed solution of Zn(NO3)2 and watermelon (Citrullus lanatus) peel extract on glass substrate. The ZnO films were then annealed at 400°C for 3h. The UV-Vis absorbance spectra show the strong absorption peaks occurs over a range of wavelengths of 220-380nm, and 190-235 nm for pre-annealed and annealed samples, respectively. The optical band gap of the samples was influenced by the heat treatment. The as-prepared samples synthesized at pH 8 is 3.73 eV and increased up to 5.4 eV after annealed at 400 °C for 3 h. This result suggested that pre-annealed sample has better photocatalytic activity compared to the annealed samples. The XRD pattern of the ZnO films exhibits the ZnO diffraction peaks that correspond to the hkl of hexagonal wurtzite structure. SEM image shows that the morphology of ZnO samples are spherical and rod-like microstructure.

In this study, the zinc oxide (ZnO) films have been prepared via the green-synthesis method with rind extract of red watermelon (Citrullus lanatus) as bio-stabilizer, at various acidity (pH) conditions. The ZnO films were prepared as thin films by spin-coating colloidal ZnO onto a glass substrate. The physical properties of ZnO films were characterized using UV-Vis spectrophotometer, XRD, SEM/EDX, and FTIR. The photocatalytic activity of ZnO films was evaluated systematically in the degradation process of methylene blue (MB). The sample prepared at pH 12 possesses the highest purities and exhibits the maximum degradation percentage of 94.61%, with a reaction rate constant of 0.019 min -1 . The efficiency of the ZnO photocatalyst has a strong correlation with the pH value in the synthesis process. Based on the results of this study, ZnO films prepared via green synthesis using Citrullus lanatus show an effective photocatalytic activity in degradation of MB, so that it could be developed in the photocatalytic process of water purification.

The power of microwave irradiation affect the quality of activated carbon. In this research the activated carbon has been made of biomass of corn cob by using carbonization process, chemical activation using potassium hydroxide as the activating agent and microwave irradiation power was variated for 360 watt, 450 watt, 630 watt, dan 720 watt in 15 minutes. The surface morphology of activated carbon for the sample KA720 produced lots of pores more than that of the sample KA360, KA450, and KA630. The sea water that has been mixed with activaed carbon using microwave irradiation power of 720 watt with temperatur of 26oC, and pH of 7,41.